1. Field of the Invention
The present invention relates to an information reproducing apparatus for reproducing information recorded on an optical disc by a mark-length recording system.
2. Description of the Related Art
Recently, optical discs in which information is recorded by a mark-length recording system have been put to practical use. According to this recording system, a block unit including a preamble part and a data part is used as a unit, and a number of block units are used for information recording. The preamble part stores a predetermined code for synchronizing the block units, and the data part stores recording data and a sync code.
There has been proposed an appartus (Japanese Patent Application No. 2-201533/90), wherein when information is reproduced from the optical disc, an average value of detection signals of the preamble portions recorded on the optical disc is found, and, on the basis of a slice level determined by the average value, the data part is digitized at a center level of the amplitude tude of the preamble part.
This apparatus exactly detects the pit width and the interval between pits and prevents erroneous data reproduction, even when a laser reflection light amount from the optical disc varies due to a focal offset of the optical head, a variation in film sensitivity of the optical disc, a variation in laser intensity, a distor tion in analog circuits and digitizing circuits, etc.
In this apparatus, however, erroneous reproduction cannot be prevented when the center of amplitude of the data part is displaced.